Wow I can't believe I forgot to answer your last VM! My bad, but answering your questions now. The main set in my opinion is Hidden Power Bug - Spikes - Toxic - Rapid Spin. Its function is basically to setup Spikes and Toxic to annoy things. Its partners are basically the standard stall mons like Raikou and Snorlax, I think in this section it would be better if you could use the knowledge you have of the metagame. 'What separates from Cloyster?' is pretty easy to answer, they are way too different! Cloyster is more of an offensive mon, in the other hand Forry is basically almost all defensive.
Feel free to ask more, but Forretress will need more than 1 set for sure. Rest, Earthquake, Sleep Talk, Hidden Power Fire, Reflect, Light Screen, Curse, and Explosion are all usable moves for that specifc mon. I suggest you to go through Forry's movepool and to study a little more, than you can make a new thread. But again: feel free to ask anything you want about it, I appreciate you ask me.